Added VmOs Provider and Name to allow using ubuntu 20.04 (#272)

Co-authored-by: Blair L Murri <BMurri@users.noreply.github.com>

docs/troubleshooting-guide.md

@@ -215,6 +215,8 @@ Configuration   parameter | Has default | Validated | Used by update | Comment
 string   SubscriptionId | N | Y | Y | Azure Subscription Id - Always required
 string   RegionName | N | Y | N | Azure region name to deploy to - Required for new install
 string   MainIdentifierPrefix = "coa" | Y | Y | N | Prefix for all resources to be deployed - Required to deploy but defaults to "coa"
+string   VmOsProvider = "Canonical" | Y | N | N | OS Provider VM to use as the host - Not required and defaults to Ubuntu
+string   VmOsName = "UbuntuServer" | Y | N | N | OS Name of the VM to use as the host - Not required and defaults to UbuntuServer
 string   VmOsVersion = "18.04-LTS" | Y | N | N | OS Version of the Linux Ubuntu VM to use as the host - Not required and defaults to Ubuntu 18.04 LTS
 string   VmSize   = "Standard_D3_v2" | Y | N | N | VM size of the Linux Ubuntu VM to use as the host - Not required and defaults to [Standard_D3_v2](https://docs.microsoft.com/en-us/azure/cloud-services/cloud-services-sizes-specs#dv2-series)
 string   VmUsername = "vmadmin"; | Y | N | Y | Username created on Cromwell on Azure Linux host - Not required and defaults to "vmadmin"

src/deploy-cromwell-on-azure/Configuration.cs

@@ -14,6 +14,8 @@ public class Configuration
         public string SubscriptionId { get; set; }
         public string RegionName { get; set; }
         public string MainIdentifierPrefix { get; set; } = "coa";
+        public string VmOsProvider { get; set; } = "Canonical";
+        public string VmOsName { get; set; } = "UbuntuServer";
         public string VmOsVersion { get; set; } = "18.04-LTS";
         public string VmSize { get; set; } = "Standard_D3_v2";
         public string VnetAddressSpace { get; set; } = "10.0.0.0/24";

src/deploy-cromwell-on-azure/Deployer.cs

@@ -1078,7 +1078,7 @@ private Task<IVirtualMachine> CreateVirtualMachineAsync(IIdentity managedIdentit
                 .WithPrimaryPrivateIPAddressDynamic();
 
             var vmDefinitionPart2 = (configuration.PrivateNetworking.GetValueOrDefault() ? vmDefinitionPart1.WithoutPrimaryPublicIPAddress() : vmDefinitionPart1.WithNewPrimaryPublicIPAddress(configuration.VmName))
-                .WithLatestLinuxImage("Canonical", "UbuntuServer", configuration.VmOsVersion)
+                .WithLatestLinuxImage(configuration.VmOsProvider, configuration.VmOsName, configuration.VmOsVersion)
                 .WithRootUsername(configuration.VmUsername)
                 .WithRootPassword(configuration.VmPassword)
                 .WithNewDataDisk(dataDiskSizeGiB, dataDiskLun, CachingTypes.None)